1. Field of the Invention
The invention relates to an arrangement for the visualization of a three-dimensional scene by means of maximum intensity projection (MIP), the arrangement comprising a display having a two-dimensional matrix of pixels; a memory for storing data representing the three-dimensional scene as a plurality of voxel values; and computing means, having access to said memory, for assigning to pixels of the display a greyvalue being a maximum of interpolated greyvalues along rays through the scene, associated with said pixels. Such an arrangement or workstation is, for example, used for inspection of images of a volume of which the distribution of a parameter is obtained in three dimensions by means of a technique such as magnetic resonance imaging or three-dimensional computed tomography. In particular, MIP is a technique often used in clinical applications of magnetic resonance angiography (MRA).
2. Description of the Related Art
With MRA, volume data is usually too noisy for providing satisfactory projection images using techniques based on extraction and shadowing of surfaces. With MIP, for each pixel of the output image a ray is casted through the image volume. The maximum greyvalue encountered along said ray, i.e. at any one of the sample positions at which the greyvalue is calculated, is used as the resulting greyvalue of the pixel.
As the casted rays or the sample points do, in general, not coincide with voxel centers, the greyvalues associated with the sample points have to be calculated from nearby voxel values. Good image quality can be obtained by trilinear (first order) interpolation of voxel values. Even better image quality can be obtained by using more complex methods of (higher order) interpolation.
First or higher order interpolations are computationally expensive operations. When floating point operations are used, calculation of an MIP image having 256.sup.2 pixels, typically requires in the order of 0.5 GFLOPS (5.times.10.sup.8 floating point operations) if a trilinear interpolation is used. On a currently commercially available workstation this represents a total processing time of about one minute. With clinical application of MIP, it is desirable to calculate multiple high-quality projection images. An often used way of presentation is in the form of a sequence of projection images with angles which differ only slightly (3.degree.-6.degree.) from each other. Since the resulting images have to be available within a short period, the high computational requirements associated with trilinear or higher order interpolation are prohibitive. In clinical practice, nearest neighbor (zero-th order) interpolation techniques that lead to inferior image quality are therefore used. Also in other possible applications a fast calculation of a high-quality image is desirable, for example, when the choice of a later two-dimensional projection is determined by what is visible in an earlier image.